There are always compromises that have to be made when designing a camera, not least when designing digital cameras for surveillance purposes. Such cameras will typically be required to operate under varying conditions and compromises that have to be made will relate to the choice of combinations of image sensor and optics. More importantly, the acceptable compromises will vary with the scene conditions for a specific camera. As an example, it may be acceptable to sacrifice spatial resolution for light sensitivity during the night, while the same camera should prioritize resolution when the light levels are higher (i.e. daytime). Similar considerations exist for other image parameters, e.g. color reproduction and frame rate (i.e. temporal resolution). The rationale for this in surveillance applications is the fact that it is better to record something in a scene, albeit with lower quality, compared to nothing at all. It also demonstrates the large gamut of conditions faced by a surveillance camera. Furthermore, technologies are often not available to handle the full range of conditions using a specific optics/sensor combination. An example would be a multi-megapixel sensor which could be used as a component in a very high-resolution camera. Ideally, the sensor should also be able to do high quality imaging in low light situations. This implies the use of a sensor with large picture elements (pixels) in order to maximize light sensitivity and dynamic range. Unfortunately, it is typically difficult to equip a camera with a multi-megapixel image sensor having large picture elements and at the same time have the option of using reasonably priced optical components in the standard form factors used for surveillance applications. This constrains component choices to geometrically smaller sensors with corresponding small pixels for a high resolution surveillance camera. So, in this use case it often becomes a matter of sacrificing low light sensitivity and dynamic range for all high-resolution camera use cases, even if it e.g. would be acceptable to use lower resolution in some situations in order to maintain sensitivity.
One way to address the issues above is of course to install several cameras looking at the same scene, but each equipped with different sensors and optics. This will however make the system more complex as well as increase installation- and maintenance costs which are constraining parameters for many surveillance installations.
Another problem, especially in high-resolution surveillance, is the need for very accurate positioning of the sensor with regard to the lens focal plane. This becomes a severe camera design constraint when pixel size goes down. Camera unit-to-unit differences with regard to mechanical tolerances in combination with impact of varying ambient temperatures compounds the problem. The resulting issues must be addressed in the design phase as well as during production, all of which of course increases product complexity and unit cost.